I just bought a 3.91 rear diff for my 2010 6MT and am trying to find a handheld tuner that:
1) has gear ratio speedometer correction in it's options, and
2a) will allow for gear ratios to be input as an open variable, or
2b) has 3.91 as a selectable ratio.

I don't have any performance shops near by that do custom tunes. I live in what some people call "fly-over country," plus, I'm going to remain basically stock and trying to keep cost down, so even if a shop was near by, I'm trying to avoid that extra expense if a handheld has the options in it already.

I have not installed the differential because I don't have this problem solved yet. So far, even the owner's manuals of various tuners don't go into enough detail as to actually address this question. I have even looked at manufactures' websites and forums and I have not found the info there either. An unnamed manufacturer answered my email by saying it "should," have the option, and if not, they would write a custom tune for me which included it. This isn't really encouraging since they couldn't even tell me if it did or not, but "should..." I guess he couldn't be bothered to go fire up one of his products in the name of some sales.

So for those of you that own a handheld with the gear ratio speedometer correction option, and an itch to help another Camaro in need, could you connect up your tuner and look through the options for the gear ratio and answer back with:
1) make and model of handheld tuner,
2) if ratio is adjustable by an open variable, as in you input the numbers, or
3a) if ratio is adjustable by selecting from several preset values, and
3b) if 3.91 is one of them?

Thanks in advance for this. I can't wait to put this issue to bed, install my diff, and actually go enjoy this upgrade.

As stated in the OP, I already know custom tunes are available, but I'm trying to avoid the expense and hassle of a custom tune if an off-the-shelf preloaded tune on an off-the-shelf tuner already has it in there.

If the off-the-shelf tune/tuner exists, I can and will buy the tuner used, which saves more money. That's what I'm after. I already know if I buy a new one from a dealer or manufacturer they would put in the custom option.

Yes, but does it allow for 3.91, specifically? You might have to fire up the Intune to look at the option because the owner's manual and website does not appear to have the answer.

Quote:

Originally Posted by ccutaia

Don't feel bad, I'm having the same problem, don't know which one will do the 3:91 gear adjustment.

Quote:

Originally Posted by niznos

As stated in the OP, I already know custom tunes are available, but I'm trying to avoid the expense and hassle of a custom tune if an off-the-shelf preloaded tune on an off-the-shelf tuner already has it in there.

If the off-the-shelf tune/tuner exists, I can and will buy the tuner used, which saves more money. That's what I'm after. I already know if I buy a new one from a dealer or manufacturer they would put in the custom option.

As I recall 3.91 is not available as an option on any off the shelf tuners.

If so this is a New option you may not find on a used tuner.

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Purchase the tuner from me and the first tune for simple bolt ons is free i.e cai and cat back the gear option on a Manual trans car is 55.00

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Since no one here has given the definitive answer I needed. I've contacted manufacturers to get at the answers I was looking for.

First, Diablosport. Mike Litsch responded to my email, stating the Intune I1000 has the 3.91 ratio as a selectable option out-of-the-box, and should not require a custom tune. Also, reading their website, it appears that a custom tune would be offered, free of charge, for the Trinity device.

Rich McKinsie of Superchips responded his device will do 3.73 and 4.10, but not our 3.91. I followed up with the fact that as this ratio becomes more and more popular, he should consider making this a selectable option and implement it through a version update so it is available across the board to even current owners. Rich said that "would require finding one in our area that is factory stock with that gear option for testing in order to make a program for it."

Lastly, I got an email reply from David Jirkovsky of SCT. He confirmed the 3.91 ratio is supported but not as a directly selectable parameter. David explained the adjustment comes through as a ratio of the stock factor. Below is the direct cut/paste of him explaining the setting:

Yes there will be support for that, but it wont be listed as 3.91, you will have to change it by percentage of increase. So whatever stock is, you would divide 3.91/(stock) and you will get a number 1.xx. That xx is your percentage increase. So if they are 3:45 stock, it would be 3.91/3.45 and that is 1.133333 so your percent increase is 13% and you would set the tuner to 113.

I followed up by asking if that is a USER selectable setting and not a custom tuner setting, and he confirmed it was USER.

So SCT WILL DO our 3.91's off-the-shelf, and without a custom tune at an added expense.

Lastly, I got an email reply from David Jirkovsky of SCT. He confirmed the 3.91 ratio is supported but not as a directly selectable parameter. David explained the adjustment comes through as a ratio of the stock factor. Below is the direct cut/paste of him explaining the setting:

Yes there will be support for that, but it wont be listed as 3.91, you will have to change it by percentage of increase. So whatever stock is, you would divide 3.91/(stock) and you will get a number 1.xx. That xx is your percentage increase. So if they are 3:45 stock, it would be 3.91/3.45 and that is 1.133333 so your percent increase is 13% and you would set the tuner to 113.

I followed up by asking if that is a USER selectable setting and not a custom tuner setting, and he confirmed it was USER.

So SCT WILL DO our 3.91's off-the-shelf, and without a custom tune at an added expense.

Just a bit of follow up for those keeping up with this. I finally installed the 3.91 diff a couple of days ago and set the speedo correction with the Diablosport InTune. I ran the car steady at various speeds from single digits up to 65+ and checked the speedo against a Garmin Nuvi GPS and they were identical.

As a sidebar, I installed BMR diff bushing BK029 and used Red Line gear oil (LSD additive not required) and I'm extremely happy with all of it.